If in the operation of the centrifugal pump at low temperature in the noise and vibration, and with the decrease of flow, lift and efficiency, sometimes even can not work, and maintenance, can often be found at the edge of the blade inlet near the pitting or cellular damage, serious when the blade has this kind of phenomenon, even blade was through, this is caused by the cavitation damage.
The reason for cavitation of centrifugal cryogenic pump: the pump works on the liquid through rotating impeller to increase the liquid energy. In the process of interaction, the velocity and pressure of the liquid change. Usually, centrifugal cold pump impeller entrance is the lowest pressure. If the place of pressure equal to or lower than the temperature of the liquid evaporation pressure, there will be a steam and gas dissolved in the liquid of a large number of escape from the liquid, forming many steam and gas mixture of small bubbles. These small bubbles, as the liquid flows into the high pressure zone, are due to the vaporization pressure inside the bubble, and the bubbles are more than the pressure of vaporization, resulting in differential pressure. Under this differential pressure, the bubbles collapse and recongeal. During the coagulation process, the liquid particles accelerate from the surrounding to the center of the bubble, and in the moment of condensation, the particle collides with each other, producing high local pressure. These bubbles, if they break down near the surface of the metal, are condensed, and the liquid mass is like numerous small warheads, continuously hitting the metal surface. The metal surface is gradually destroyed by fatigue, which is often called denudation, in a continuous strike with high pressure and high frequency. There are some active gases (such as oxygen, etc.) in the generated bubbles, which are chemically corrosive to metals by the heat released by the condensation of the bubbles. The joint action of chemical corrosion and mechanical denudation has accelerated the speed of metal damage, which is the phenomenon of cavitation damage.
When the centrifugal cryogenic pump begins to produce cavitation, the cavitation area is small, and there is no obvious effect on the normal operation of the pump, and there is no obvious reflection on the pump performance curve. However, when the cavitation develops to a certain extent, the bubbles are produced in large quantities, which affect the normal flow of the liquid, and even cause the fluid flow to break, producing vibration and noise. At the same time, the flow rate, lift and efficiency of the pump are obviously decreased, and the pump performance curve also has obvious performance. When serious, the pump cannot work. Articles by hangzhou zed pump as much as possible in order to avoid cavitation phenomenon, in the process design, should make the liquid before into the pump has a certain degree of supercooling, at the same time, the pump body to install in a lower position, make the liquid inlet has a certain number of static head. In addition, it is necessary to protect the cold and minimize the loss of cold.